This invention relates to a dispensing apparatus for dispensing pressurised fluid in the form of an aerosol and in particular but not exclusively for dispensing medicine or products in solution or suspension in an alcohol base.
It is known from GB-1201918 for example to provide dispensing apparatus in which pressurised fluid from a pressurised dispensing container is released by a valve in a controlled manner, the valve including elastomeric seals which are annular and which co-operate with a sliding valve stem to open and close fluid ports.
Products to be dispensed are commonly provided in solution or suspension in an alcohol base, this being particularly common in the dispensing of medicinal compounds for inhalation therapy.
Typical apparatus includes a CFC volatile propellant having a liquid phase in which the product together with the alcohol carrier is readily soluble within the container and a typical material for the valve seal is a synthetic rubber such as nitrile rubber.
Recent trends in the production of aerosol dispensers have moved away from CFC propellants because of their environmental hazards and HFC propellants are now being introduced. A problem with such propellants is that alcohol is less soluble in the liquid phase of such propellants and tends to separate within the container thereby exposing the valve seals to a much greater concentration of alcohol than was formerly the case. Seal materials such as nitrile rubber allow alcohol vapour to escape by permeation over extended storage periods so that the remaining quantity of alcohol is significantly depleted.
It is an object of the present invention to provide dispensing apparatus which will allow the use of HFC propellants with alcohol based products without the above disadvantage.
According to the present invention there is disclosed dispensing apparatus for dispensing pressurised fluid comprising a valve body defining a chamber, a valve member extending movably through the chamber and through at least one annular seal co-operating with the valve member and the body to regulate the discharge of fluid, wherein the or at least one of the seals is formed from a material comprising (a) a copolymer of ethylene and propylene or (b) a terpolymer of ethylene, propylene and a diene, or (c) a material selected from isobutylene isoprene, polychloroprene or a fluorinated rubber.
It has been found that the extent to which alcohol evaporates from such apparatus using such seal materials is significantly decreased so that typically a required shelf life of three years can be readily achieved.
Preferably the material comprises a peroxide curing agent.
A peroxide curing agent such as dicumyl peroxide is preferable to other curing agents such as sulphur since its use minimises the formation of extractives (e.g. 2-mercaptobenzothiazole, N-nitrosamines, mercaptobenzothiazole disulphide) resulting from contact between the material and alcohol in use.
Preferably the seal material comprises a mineral filler.
Mineral fillers are preferable to carbon black in order to minimise the formation of polynuclear aromatic hydrocarbon compounds.
Advantageously the mineral filler is selected from the group comprising magnesium silicate, aluminium silicate, silica titanium oxide, zinc oxide, calcium carbonate, magnesium carbonate, magnesium aluminium silicate, aluminium hydroxide, talc, kaolin and clay. Preferably the filler is magnesium silicate or kaolin.
Preferably the apparatus comprises a pressurised dispensing container operatively connected to the valve body and containing the fluid to be dispensed and a hydrofluorocarbon propellant comprising propellant type 134a or 227.
(The designation of propellant types referred to in the present application is as specified in British Standard BS4580:1970"Specification for number designations of organic refrigerants". Accordingly, propellant 134a is:
1,1,1,2-Tetrafluoroethane CH.sub.2 F--CF.sub.3 and propellant 227 is: PA0 1,1,1,2,3,3,3 Heptafluoropropane CF.sub.3 --CHF--CF.sub.3).
Typically the fluid to be dispensed comprises a liquid or particulate product as a solution or suspension in a carrier liquid comprising an alcohol such as ethanol.